Wow, 52 RHR / 52-60 during sleep lagi low sia. Technically that usually points to great aerobic fitness in an athletic pax........but of coz for the general population that's a bit on the low side, but usually nothing to worry about.
Setting zones correctly ah.....that's the somewhat tricky part and often a hot topic for debate. Of coz at your current level of 140+ bpm with just walking, just focus on building your base, make it a priority of healthy lifestyle first. It's really a priority choice vs career esp. Bo bian one, whole mindset need to change if it's for sports, 180 deg change. I know the feeling, i used to be a total wuss last time also regarding fitness/sports.
So, just run for fun first and slowly build volume and even a bit of speed (you will improve with consistent sessions one, these are called beginner gains) , once exercising sessions are prioritised and consistent then you can start to analyze more data.
After the foundation has been built, then just do a LTHR run test when you feel your running is in the more intermediate stage, youtube a lot of egs. Your watch shd have this feature.....probably your Garmin already is showing you a rough guesstimation coz you "have been running hard enough".
If you gain fitness significantly, your training zones also change if not you'll be undertraining at lower intensities as you go by.........so need to be tested somewhat occasionally. If you dont feel any significant changes, then no need to test.
If you are not keen to do this LTHR test coz it takes a whole 30-40 mins in total and since it is a threshold kinda sustained test that needs pacing and whatnots, some folks (those who dont like periodized 80/20 training) might not like it, then maybe invest in a lactate meter....TB got meter and test strips, sufficiently zhun and decently priced, then things can be done faster and not at LTHR prolonged intensities.
Personally, if you are one who later finds data to be very important and you are able to stick to structured training and you are really after performance goals (maybe next year?), i find the lactate meter to be good to use and more convenient, more objective coz it is less prone to errors, you just need to bite the bullet, TB got options under $300 nia, not expensive compared to other gadgets or some folks even spend much more on their sports hobbies. For running a bit leceh to bring out but if you test around your neighbourhood it shd be fine. Cycling no issue coz back pockets. LT1 and LT2 levels are different between running and cycling.
Of coz there's also this issue about poking (each test needs at least like 4-6 pokes even if you start near your your known LT points in prev tests) but if you have done blood glucose tests before it's a non issue lah.
Wah....you like to push till MHR ah, 193-195.
Here's one more thing which i feel is also quite important.....I'd really advise at least a basic ECG checkup if you are really serious about getting into sports. At least basic check for arrhythmias or possibly even prev silent heart attacks or any other cardiac issues also good. GP can do already, well under a hundred bucks.
The next one is better still, treadmill ECG test, the added stress shd be able to tease out issues if they are hiding and not visible when at rest....coz ultimately, you ARE doing sports that require high cardiac demands.
Not only the ECG is checked upon, but the profile regarding BP and HR rise with each step up is appropriate, in which the ECG would not tell you.
Bo bian....make it a hobby as well, in addition to lifestyle change. For me i find cycling more enjoyable than running.....and running does help cycling as well. 15-20 hrs per week on training (overtraining more like lol

) possible , esp if you go out with kakis or family members (i go out with my kid on weekends) If you find it enjoyable rather than just a new year goal that you set and wanna hit, then it goes far beyond the technicalities of what is being mentioned in this thread.
Also, cycling on the roads quite happening one, if you should find that you cycle at say 8+pm, you will find that you will be pushed hard often at times just for survival, unstructured intervals that tests all various paces one. heh.... Then you will literally enjoy LT2, VO2max and even sprint paces.